Ken Griffey Jr. has what many consider to be among the finest-looking swings of his generation. It's a swing synonymous with Mariner baseball, a swing smoother than an unfolded emergency survival blanket and a swing after which couples name their children. Through five months of the season, he's hitting .221/.329/.399 with a .322 wOBA.
Mike Sweeney swings like someone just blew an air horn. Through five months of the season, he's hitting .262/.316/.417 with a .315 wOBA.
Having pretty swing mechanics can be useful, but it's separated from actual production by so many levels as to be borderline irrelevant. Provided a guy surpasses a minimum level of acceptability in that regard, it seems to me the only real concern should be the speed with which the bat clears the zone.